The present invention relates generally to apparatus and methods for making molded products, and in particular, methods and apparatus primarily intended for making components of oil seals or the like.
In one application, a mold made according to the present invention is able to form and bond an elastomeric collar or cylinder of a desired contour onto the axially extending flange of a cylindrical metal casing to provide a finished or finishable oil seal part, without leakage or flash of the elastomer from the mold and without inducing objectionable dimensional variation in the casing forming a part of the finished product.
According to the invention, a multi-part mold is provided which, in use, operates through a definite sequence serving to preposition and then locate the casing in a desired position of initial use. Thereafter, as the mold continues to close, a "prep" or preformed portion of uncured elastomer is forced from a pocket or shelf area into a molding cavity defined by a portion of the casing and portions of the mold core and the mold top insert, respectively. As mold closure movement continues, the casing continues to be supported by a bottom insert and the bottom insert slides slightly relatively to the mold core. This positions the lower, reduced thickness margin of the casing between parts of the mold core and the lower insert and imparts a pinching action sufficient to cause these mold parts to establish and maintain a flash barrier.
Further relative movement of the mold parts closes the cavity completely and causes the mold core to begin "floating" downwardly. Finally, in the fully closed position of the mold, the top plate and the lower plate have most closely approached each other and certain of the mold parts are in a "solid height" or fully closed relationship as the molding press platens complete their stroke. At this point, both the mold core and the lower insert have moved within the intended limits of their travel so as to have created and maintained the flash barrier and yet have allowed for relative movement of the casing so as to establish the flash barrier not only along the skirt, but also at the corner of the casing. This upper or second flash barrier is created by impingement of a land on the top insert on a corner of the casing as mold closure begins and as elastomers begin flowing into the cavity.
When the cavity has assumed its final dimensions, after the flash barriers have been formed, the elastomer is permitted to cure for a short time, typically one to three minutes or more at an elevated temperature of perhaps 325 degrees F., for example. Thereafter, the mold opens and the part may be removed. In the opening sequence, the forces generated by the springs which respectively support the lower insert and the core for limited movement are gradually released and the shoulder on the stripper plate lifts a counterpart shoulder on the stripper ring, acting upwardly upon the casing radial flange to remove it from its position atop the nose of the bottom insert.
When the mold is completely open, those portions associated with the cover plate, which include the mold top plate, top insert, and certain auxiliary parts, are spaced well apart from the lower sections of the mold and the casing is supported on the stripper ring. Thereupon, the finished part may be removed from the mold, a new casing inserted, a new prep positioned in the indicated area, and the mold closure may begin with the molding cycle being thereafter repeated.
An important feature of the present invention is the provision of certain precisely formed surfaces which engage each other and/or the casing to achieve a desired operating sequence. Provision of springs which support the bottom insert and the core respectively for movement relative to each other and to the bottom cover plate is also an important feature of the invention. According to the invention, tapered surfaces are provided to support the casing skirt and barrier surfaces are placed adjacent those surfaces of the mold core which define a portion of the cavity. The top insert preferably includes a land adapted to engage the corner portion of the casing to provide an upper flash barrier.
In the following specification, it is assumed that the press is a so-called down-acting press and that the casing skirt extends downwardly from the radial flange. Certain of these parts might be reversed with equal effect under some circumstances and consequently, the description given herein is intended to embrace both forms of apparatus.
In view of the failure of the prior art to provide a totally satisfactory method of making seal components such as wear sleeves or the like requiring flash barriers along essentially the same axial surface, it is an object of the present invention to provide an improved multi-part mold for insert molding of casings and elastomer-forming materials.
Another object of the invention is to provide an improved mold wherein the mold core and the mold bottom insert may move relative to each other as a part of the mold closing stroke.
A further object of the invention is to provide a mold wherein a stripper ring is positioned for support by and movement relative to a bottom insert whereby advantage may be taken of positioning the casing as desired during molding and removal of the casing as a part of a finished product after the molding cycle has been completed.
A still further object of the invention is to provide an array of mold parts constructed and arranged so that the mold parts which, in the closed position of the mold, form parts of the cavity or support the casing, are engaged by springs normally biasing the parts to an open position, while other parts, in the closed position, engage each other to form a positive stop or "solid height" to limit mold part movement.
Yet another object of the invention is to provide a mold assembly which includes a core having cavity-forming surfaces, a prep receiving surface, and barrier surfaces adapted to cooperate with a seal casing in the use of the mold, which core surface is mounted for limited movement against a predetermined resistance during its operational cycle.
Another object of the invention is to provide a mold unit in which the mold core and the bottom insert move not only relative to the bottom cover plate of the mold but also relative to each other during mold closing and opening, and wherein both the bottom insert and the mold core are mounted for resilient movement.
A further object of the invention is to provide a bottom insert and a mold core which move relative to each other, with one of such parts including a flash barrier surface and the other including a casing support surface adapted to position a casing skirt between them for positively locating the skirt during establishment for a flash barrier.
A still further object of the invention is to provide a mold which includes a top insert having a plurality of pockets for positioning a spring loaded, relatively movable plunger acting to locate the casing during portions of the mold operating cycle to insure proper positioning of the casing during initial portions of the movement cycle.
Yet another object of the invention is to provide a multi-part mold in which the top insert includes not only means for engaging and retaining a casing in a desired position of use during initial mold closing, but which includes a barrier land engageable with a portion of the casing at or near the beginning of the mold stroke.
Another object of the invention is to provide a method of molding a seal part or element which includes a margin forming a part of the skirt casing, which method includes supporting the margin along a tapered mold part supporting surface, engaging the casing so as to position it relative to a mold part such as a bottom insert and thereafter moving the casing such that one surface of the casing margin moves into position and engages a barrier surface on an adjacent mold part in fluid tight relation as a part of the closing movement cycle.
Yet another object of the invention is to provide a mold assembly having, in one form, a core and a lower insert separately supported for movement relative to each other and to the other mold parts by engagement with resilient spring elements, and having, in another form, top and bottom insert parts of the mold engaged by springs during mold closure, and in both forms of which the axial flange of a casing moves between a part of the mold core and the lower insert to establish one of the flash barriers.
A still further object of the invention is to provide mold parts which are constructed and arranged to establish flash barriers on both ends of an axially extending casing or like member, and wherein such barrier surfaces are established and maintained during a measurable part of the mold closing stroke.
A further object of the invention is to provide a method which includes forming a seal part in a multi-part mold wherein one mold part which includes a barrier-forming surface and mold cavity defining surfaces moves during closing relative to another mold part which supports the casing from an opposite side thereof to provide a portion of the action forming the flash barrier.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a multi-part mold which includes a mold core and lower insert movable relative to a fixed mold part and relative to each other, and in which one such part supports and positions the casing during mold closure and wherein the other mold part includes a barrier-forming surface as well as a portion of the cavity forming surface, such mold parts cooperating with other portions including a top insert having a flash barrier land thereon, whereby, in use, a flash free part may be formed in the use of the mold. The objects and advantages of the invention are also carried into practice by a method which includes positioning a casing such that the flash barrier surfaces may be formed on the casing margin by moving the margin into a space between relatively movable mold parts, with both of these mold parts or other cooperating parts being supported for limited movement against resilient biasing means during mold closing.
The manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings wherein like reference numbers indicate corresponding parts throughout.